He made his debut in 1997 as the character Git Hynes in the Irish comedy I Went Down, co-starring alongside Brendan Gleeson. McDonald wrote and directed Pentecost, a live action short film which was nominated for the 2012 Academy Award for Best Live Action Short Film. He also co-wrote and acted in the full length movie, The Stag, which was nominated for six Irish Film and Television Academy (IFTA) awards in 2014.